Roughly 1.5 million US men living today have been treated with radiation therapy for prostate cancer and the number is expected to increase. The majority of these patients will suffer significant reduction in quality of life (i.e., erectile dysfunction, incontinence and proctitis) ad there are no FDA approved treatments to protect normal pelvic tissues from radiation-induced damage. Radiation exposure leads to free radical-mediated oxidative damage to normal tissues leading to fibrosis. The activation of p300 helps to drive persistent inflammation and fibrosis after irradiation. Cancer cells have increased metabolic production of reactive oxygen species (ROS) and p300 activity, relative to normal cells, which have been shown to drive cancer progression. Thus, suppressing radiation-induced ROS and p300 activity can act as both a radio-protector in normal tissues while inhibiting pro-survival and progression pathways in cancer cells. MnTE-2-PyP is a small molecule antioxidant, which scavenges a variety of ROS and reduces p300 activity. Preliminary data demonstrate that MnTE-2-PyP protects urogenital tissues from radiation-induced damage, while enhancing prostate cancer killing. The overall hypothesis of this proposal is that MnTE-2-PyP both scavenges ROS and inhibits p300 activity, which protects normal tissue injury by suppressing fibrosis while at the same time inhibiting tumor progression. Specific Aim 1 will determine whether MnTE-2-PyP protects normal pelvic tissues from radiation-induced inflammation by inhibiting both NADPH oxidase derived ROS and p300 activity. We will determine whether: 1. MnTE-2-PyP protects normal tissues from radiation damage by inhibiting ROS and p300 2. MnTE-2-PyP through ROS scavenging and p300 inhibition prevents pro-fibrotic signaling in fibroblasts exposed to irradiation 3. MnTE-2-PyP protects normal tissues by inhibiting Th2 inflammatory response by inhibiting NADPH oxidase- derived ROS and p300 activity. Specific Aim 2 will determine whether MnTE-2-PyP inhibits the progression of irradiated prostate cancer cells both in vitro and in vivo via ROS scavenging and p300 inhibition. In this aim it will be demonstrated that: 1. MnTE-2-PyP sensitizes prostate cancer cells to irradiation in vitro and in vivo 2. The manipulation of p300 and/or ROS affects the ability of MnTE-2-PyP to inhibit pro-survival and pro-angiogenic pathways necessary for tumor survival. 3. MnTE-2-PyP inhibits tumor growth and metastasis in an irradiated orthotopic xenograft model while protecting normal tissues. The completion of the studies will provide an in depth mechanistic understanding of the mechanisms by which MnTE-2-PyP inhibits normal tissue injury, while reducing prostate cancer growth during prostate cancer radiotherapy. Understanding how MnTE-2-PyP works as a radio-protector, can lead to the development more targeted therapies to enhance treatment outcomes in prostate cancer radiotherapy.